Stages of decomposition

Whale falls undergo different faunal successions described here as stages. Each stage has its own unique assemblage of organisms and has its own role in the breakdown of the carcass. Fauna and time frames differ between deep-sea whale falls, mid depth and shallow sea whale falls but they all undergo the 4 stages of faunal succession.

Stage 1: Mobile Scavenger

Stage 2: An enrichment opportunist stage

Stage 3: A Sulphopilic stage

Stage 4: Reef Stage

Figure 1. Artists impression of stage 1

Stage 1 can last for several months or even a few years depending on the size of the whale. This stage is the fastest of the stages and attracts the most mega fauna. These species are mainly fish and crustaceans (Goffredi et al, 2004).

            It is at this stage in which most of the soft tissues are removed. Notable larger species include hagfish, sleeper sharks, rat- tails, cephalopods. (Smith et al 2003)

Stage2 involves the bioturbation of the surrounding sediments. This is a result of the dead organic matter littering the floor. Already the bones are beginning to become covered in chemosynthetic bacteria. Most of the sediment is used by invertebrates i.e polychaetes and crustaceans. The sediments are also littered with sulphur loving bivalves that contain chemosynthetic bacteria. (ref) Bacteria feed of the highly rich organic matter that has fallen to the sediment from the carcass; the bacteria form a ring around the whale carcass showing the outline. This occurs due to the decomposition of the blubber releasing organic matter. The bacteria are then fed upon by other species. (Goeffredi et al 2004)

Figure 2. Osedax spp on whale bone

Stage 3 is the breakdown of the marrow and bones themselves. Bacteria start breaking down the sulphur compounds in the bones, and lipids. Whales have high concentrations of lipids in there bones to produce buoyancy. Depending on the size of the skeleton this stage may take decades. Annelid worms of the genus osedax, (zombie worm) feed on the marrow’s high lipid content. By burrowing its roots into the bone, the roots contain chemosynthetic bacteria that break down the lipids and sulphur compounds sustaining the worm. Bacteria also grow on the whale bones cleaning any residue of organic matter from the surface of the bones and slowly degrade the bones themselves. The bacteria mats are so extensive they can support a diverse community similar to those found at hydrothermal vents. This stage can last for several years. (Smith et al 1998)

Stage 4 Most sessile animals need a hard substrate on which to settle. In the deep sea these habitats are few and far between. The minerals left in the whale bones can be sufficient enough to support sessile organisms (Smith & Baco, 2003). Most sessile organisms rely on suspension feeding, this include anemones, cold water corals and sponges. The corals especially hard corals secrete calcium carbonate, this means that even after the whale bones have been completely broken down or buried in sediment. There is still a hard substrate on which the organisms can grow. This building of a biogenic reef increases biodiversity. The whale skeleton could maintain this habitat for decades.

Leave a Reply